Method and apparatus for ultrasonic peening of annular recesses for the attachment of blades to a rotor

Abstract

The invention relates to a method for the ultrasonic peening of annular recesses for the attachment of blades to a rotor rim, these recesses including a blade introduction opening. According to the method, a plurality of beads is placed on a vibratory surface of a sonotrode, arranged in an intermediate position in a sleeve having opposed closing-off means capable of sliding in the recess, the introduction opening is placed facing the sonotrode, the sonotrode and the sleeve are moved together toward the introduction opening into a peening position in which the closing-off means face the recess ends opening into said opening, then the rotor rim is turned about its axis so as to bring the closing-off means into a first end of the recess so as to form a closed chamber containing the beads. The rim is turned and the vibratory surface is vibrated to mobilize the beads within the chamber, thereby peening the recess.

We claim:  
     
       1. A method of surface treating and compressively prestressing by peening a wall of at least one annular recess approximately in the shape of a dovetail, formed in the periphery of a rotor rim, said annular recess opening to the outside via an annular lateral mouth and having at least two recess ends opening into, respectively, at least one blade introduction opening, said method comprising the steps of: 
       a) providing a sonotrode arranged within a sleeve, said sonotrode having a vibratory surface and ultrasonic means for vibrating said vibratory surface, and said sleeve having opposed closing-off means capable of sliding in the recess;  
       b) placing a plurality of beads of a predetermined diameter on said vibratory surface of said sonotrode with said sonotrode arranged in an intermediate position in which said sleeve surrounds said vibratory surface;  
       c) placing said introduction opening facing said sonotrode;  
       d) moving said sonotrode together with said sleeve substantially vertically toward said blade introduction opening to place them in a peening position in which said closing-off means face said recess ends that open into said opening;  
       (e) turning said rotor rim about an axis of rotation arranged horizontally in such a way as to bring said closing-off means into a first recess end so as to form a closed moving chamber containing said beads; and  
       f) operating said ultrasonic means to vibrate said vibratory surface of said sonotrode whereby said beads are mobilized in said moving chamber, and, by uniformly turning said rotor rim about said axis of rotation until said second recess is reached, ultrasonically peening the entirety of said wall of said recess.  
     
     
       2. A method according to  claim 1 , including the step of moving said sonotrode substantially vertically so that said vibratory surface is level with said lateral mouth of said recess, after the step of moving said sonotrode and said sleeve together into said peening position. 
     
     
       3. A method according to  claim 1 , wherein said peening step is conducted at least three successive times on said wall by reversing the direction of rotation of said rotor rim each time one of said recess ends is neared. 
     
     
       4. A method according to  claim 1 , including the step of placing a deflector in said moving chamber. 
     
     
       5. A method according to  claim 1 , further including the steps of: 
       rotating said rotor part about said axis of rotation so as to bring said closing-off means into said blade introduction opening after peening said first recess;  
       moving said sonotrode and said sleeve substantially vertically toward a lowered position;  
       moving said sleeve and said sonotrode together substantially horizontally toward an introduction opening of a second annular recess;  
       bringing said opening up to face said sonotrode; and positioning said sonotrode, supporting said beads, and said sleeve in said raised peening position to peen said second annular recess.  
     
     
       6. A method according to  claim 1 , wherein said predetermined diameter of said beads exceeds 0.8 mm. 
     
     
       7. An apparatus for use in carrying out the method according to  claim 1 , comprising a sonotrode mounted in a sleeve equipped with closing-off means, said sonotrode being capable of projecting beads of a predetermined diameter into a moving chamber delimited by a wall portion of said annular recess, said vibratory surface of said sonotrode, arranged near said mouth of said recess, and said closing-off means; 
       means for producing ultrasonic oscillations capable of exciting said sonotrode;  
       first means for moving said sonotrode substantially vertically; and  
       second means for moving said closing-off means substantially vertically;  
       a first clearance, smaller than said diameter of said beads, being formed between said sonotrode and said sleeve; and  
       a second clearance, smaller than said diameter of said beads, being formed between said closing-off means arranged in said annular recess and said annular recess.  
     
     
       8. An apparatus according to  claim 7 , wherein a third clearance, smaller than said diameter of said beads, is formed between said mouth of said recess and said vibratory surface arranged in said mouth. 
     
     
       9. An apparatus according to  claim 8 , wherein a fourth clearance, smaller than said diameter of said beads, is formed between an end of said sleeve and said mouth. 
     
     
       10. An apparatus according to  claim 7 , wherein said second means for moving said closing-off means are capable of moving said closing-off means and said sonotrode at the same time. 
     
     
       11. An apparatus according to  claim 7 , wherein said first means for moving said sonotrode and said second means for moving said closing-off means can be operated simultaneously. 
     
     
       12. An apparatus according to  claim 7 , which further comprises support means for supporting said rotor rim that is to be treated, and means for driving said support means to cause said annular recess to rotate uniformly. 
     
     
       13. An apparatus according to  claim 7 , which further comprises means for driving said plurality of beads from said vibratory surface toward a reservoir. 
     
     
       14. An apparatus according to  claim 7 , which further comprises means for moving said sonotrode and said sleeve substantially horizontally.